/*
 * Copyright (c) 2006 Your Corporation. All Rights Reserved.
 */

/**
 * Copyright 2007 Jason Horman, Pete Aykroyd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.functor.expression;

public abstract class AbstractPredicateExpression extends AbstractExpression implements PredicateExpression {
	private transient Not not;

	public OrImpl or(PredicateExpression or) {
		return new OrImpl(this, or);
	}

	public AndImpl and(PredicateExpression and) {
		return new AndImpl(this, and);
	}

	public PredicateExpression not() {
		if (not == null)
			not = new Not(this);
		return not;
	}

	public boolean isAlwaysTrue() {
		return false;
	}

	public boolean isAlwaysFalse() {
		return false;
	}

	public void modified() {
		super.modified();
		not = null;
	}
}
